The present invention is directed to an improved method for the manufacture of the corresponding nitrile produced during the ammoxidation of an unsaturated hydrocarbon selected from the group consisting of propylene and isobutylene. In particular, the process of the present invention is directed to an improvement in the recovery and purification process for acrylonitrile and methacrylonitrile.
In general, the recovery of acrylonitrile or methacrylonitrile produced by the ammoxidation of propylene or isobutylene on a commercial scale has been accomplished by contacting the hot reactor gaseous effluent containing the corresponding nitrile with an aqueous stream in a column (quench column) to cool the reactor effluent, passing the cooled gaseous stream containing the corresponding nitrile resulting to a second column (absorber column) where a second aqueous stream and the cooled gaseous stream are contacted in a counter-current flow and substantially all of the acrylonitrile or methacrylonitrile are absorbed into the second aqueous stream. This second aqueous stream containing substantially all of the acrylonitrile or methacrylonitrile is then subjected to further recovery and purification steps.
Typical recovery and purification procedures for acrylonitrile and methacrylonitrile are set forth in detail in U.S. Pat. Nos. 4,234,510 and 3,885,928 herein incorporated by reference. In addition, the above mentioned '510 patent discloses that indirect contact cooling of the gaseous effluents exiting the quench column prior to entry into the absorber column produces a considerable amount of nitrile condensation. This condensed liquid consisting mainly of the corresponding nitrile can be fed directly to the recovery and purification columns by passing the absorber column thereby decreasing capital and operating costs in the absorber operation. The use of an indirect contact cooling step can lead to the condensation of more than 50% of the corresponding nitrites which means that a majority of the corresponding nitrile may be fed directly into the recovery and purification column by passing the absorber operation.